Are you meaning heat pipe coolers, or water cooling radiators? If heat pipes, there are a few threads around that explain this, but different methods can be used for heatpipe coolers.
For watercooling, the radiator fins have no contact with the water or coolant and in most instances, are soldered to the tubes, so even aluminum fins are used.
In most real watercooling loops, there is only distilled water and some biocide of some kind. Some people use coolants that are glycol-based, similar to car antifreeze, but it is less effective. Some additives even particulate out and collect in the pin matrices of water blocks.
I guess your question is somewhat confusing...what are you actually trying to determine?
The liquid in a heat-pipe is used to transfer the heat to the cooling fins. The liquid evaporates (when heated) to transfer the heat and then condenses to bring the liquid back to the heat source, rinse/repeat.